A known autostereoscopic display device is illustrated in FIG. 1. This known device 1 comprises a two dimensional liquid crystal display panel 3 having a row and column array of display pixels 5 acting as a spatial light modulator to produce the display. For the sake of clarity, only a small number of display pixels 5 are shown in FIG. 1. In practice, the display panel 3 might comprise about one thousand rows and several thousand columns of display pixels 5.
The structure of the liquid crystal display panel 3 is entirely conventional. In particular, the panel 3 comprises a pair of spaced transparent glass substrates, between which an aligned twisted nematic or other liquid crystal material is provided. The substrates carry patterns of transparent indium tin oxide (ITO) electrodes on their facing surfaces. Polarising layers are also provided on the outer surfaces of the substrates.
Each display pixel 5 is associated with a switching element, such as a thin film transistor (TFT) or thin film diode (TFD). The display pixels are operated to produce the display by providing addressing signals to the switching elements, and suitable addressing schemes will be known to those skilled in the art.
The display panel 3 is illuminated by a light source 7 comprising, in this case, a planar backlight extending over the area of the display pixel array. Light from the light source 7 is directed through the display panel 3, with the individual display pixels 5 being driven to modulate the light and produce the display.
The display device 1 also comprises a lenticular sheet 9, arranged over the display side of the display panel 3, which performs a view forming function. The lenticular sheet 9 comprises an array of lenticular elements 11 extending parallel to one another, of which only one is shown with exaggerated dimensions for the sake of clarity.
Thus, an array of elongate lenticular elements 11 extending parallel to one another overlies the display pixel array, and the display pixels 5 are observed through these lenticular elements 11.
The lenticular elements 11 act as a light output directing means to provide different images, or views, from the display panel 3 to the eyes of a user positioned in front of the display device 1. The above described device provides an effective three dimensional display device (if the image comprises multiple views).
In an arrangement in which, for example, each lenticular element 11 is associated with two columns of display pixels 5, the display pixels 5 in each column provide a vertical slice of a respective two dimensional sub-image. The lenticular sheet 9 directs these two slices and corresponding slices from the display pixel columns associated with the other lenticular elements 11, to the left and right eyes of a user positioned in front of the sheet, so that the user observes a single stereoscopic image.
The lenticulars are mounted in front of the display and need to be aligned accurately with respect to the pixels in order to project the correct pixel information. For the same reason the dimensions of the lens array, such as the pitch and the lens shape, need to be maintained during thermal cycles. This presents difficulties in the design and manufacture of the lenticular lens array.
Examples of manufacturing techniques for lenticulars are replication techniques such as UV-replication, in-mould pressing (compression moulding) and embossing. Direct structuring methods can also be used, in which a polymer plate is shaped by laser ablation. Reflow methods are also known in which the lens shapes are defined by a melting and re-solidification process.
Compared to glass, the thermal coefficient of expansion of polymers is high, for example 200-700.times.10.sup.−7/.degree. C. for plastic and 60-120.times.10.sup.−7/.degree. C. for glass. This high thermal coefficient of expansion results in unacceptable dimensional and alignment inaccuracies of the lenticular, resulting in poor 3D performance.